a) Field of the Invention
This invention relates to a method and system for the determination of a quality of a bonded area in a boxmaking blank with opposite end portions thereof bonded together at the bonded area. In a boxmaking apparatus for continuously assembling boxes from such blanks, the above method and system makes, based on a width of a gap formed in the bonded area of the boxmaking blank, a determination as to whether the bonded area is good or bad.
b) Description of the Related Art
In a boxmaking process for producing boxes (corrugated fibreboard containers) from corrugated cardboard blanks (corrugated fibreboard blanks), it has been the conventional practice to fold each corrugated cardboard blank of a predetermined size, which includes slots formed therein and carries ruled lines, prints and the like applied thereon, to apply a glue on an overlap formed on one of opposite end portions of the corrugated cardboard blank and then to bond the opposite end portions together via the glued overlap, all by a folder gluer.
After the corrugated cardboard blanks already folded and bonded by the folder gluer are corrected in squareness at a squaring unit, they are fed out box after box from a lower part of the squaring unit to a counter unit, where they are bundled in a desired number per bundle and are then ejected.
As is shown in FIG. 13A, for example, each corrugated cardboard blank 1 is provided with gaps 1D in parts of a top flap 1A and bottom flap 1B, respectively, at locations corresponding to a bonded area 1C between opposite end portions of the blank. It is to be noted that, concerning the bonded area 1C and the gaps 1D, the overlapping back-side blank is shown with a portion thereof cut away in FIG. 13B because the bonded area 1C and the gaps 1D are located on the back side of the bonded blank and are hardly visible.
Upon bonding the corrugated cardboard blank at the area 1C, control is performed so that, as is illustrated in FIGS. 13A and 13B, width a,b of the gaps 1D have a predetermined constant value. Namely, production of a corrugated cardboard box of an accurate shape free of off-squareness requires to bond opposite end portions of a blank together in a proper positional relationship. Whether the bonded area of the blank is good or bad can be determined depending on the width of the gap corresponding to the bonded area. It is therefore important to control the gap at a predetermined width.
Attempts have therefore been made to measure the width of such gaps in an automated contactless manner in the course of boxmaking. For example, Prime Technology Inc., Maryland, U.S.A. has already commercialized a system under the name of "Gap Watch system". Further, JP kokai 9-22464 discloses a gap quality determination system making use of a CCD (charged coupled device) camera.
According to such conventional technology, a still image of a bonded area is formed by using a stroboscope or the electronic shutter function of a CCD camera and is then subjected to so-called image processing to extract necessary information.
Described specifically, the system disclosed in JP kokai 9-22464 forms a varied-density image of the bonded area and, based on differences in density, detects edges in the bonded area and determines the width of the gap in the bonded area. In other words, when light is irradiated onto a corrugated cardboard blank, stronger reflection of light is available from a gap-free area of a corrugated cardboard blank, while weaker reflection of light is obtained from its gap-containing area. This system therefore detects a gap by making use of this difference in the intensity of reflection of light occurred for the existence and non-existence of the gap.
However, an attempt to detect a gap from a varied-density image of a bonded area of a corrugated cardboard blank involves a potential problem that, when there is a print on a surface of the corrugated cardboard blank, the printed area may also be extracted erroneously as a gap depending on the color of the print because the printed area is also different in color density and hence in the intensity of reflection of light from a ground color of (a color of a liner on) the corrugated cardboard blank. Accordingly, this system must further perform accurate distinction of a true gap from the gap information so obtained.
Further, the liner color is available with considerably wide variations in color tone, ranging from a very light tone called "white liner" to a significantly dark tone called "K liner". This may result in a variation in the quantity of reflection of light from the surface of a liner in a gap and hence in the density of the surface of the liner in the gap, thereby possibly making it difficult to accurately discriminate a difference from the density of the gap. As a consequence, the measurement of the width of a gap in a bonded area, said measurement performing image processing such as edge extraction by using a varied-density image of the bonded area, has difficulty in making determination at high reliability.